Remote control apparatus

ABSTRACT

A first carrier signal generator (15) generates a carrier signal (S1) at a first frequency to modulate a preset identification code (S). A second carrier signal generator (16) generates a carrier signal (S2) at a second frequency, distinct from the first frequency. A modulator (14) affixes the identification code (S) to the carrier signal (S2), and outputs the carrier signal (S2) to a light-emitting circuit (17). When a &#34;smart&#34; or &#34;learning&#34; remote controller, of the type that demodulates frequency, receives the identification code (S), the carrier signal (Sw) of the second frequency is demodulated at the first frequency, compressed and stored in memory. The carrier signal (S2) set at the second frequency can cause the memory capacity of the remote controller to overflow, thereby preventing the identification code (S) from being stored in the learning remote controller.

TECHNICAL FIELD

The present invention relates to a remote control apparatus designed toprevent the copying of an identification code output from a transmitterconstituting the remote control apparatus.

BACKGROUND ART

For automobiles with power assisted door locks, the doors of theautomobile are locked or unlocked by a locking mechanism operated by amotor provided in a door. Door locking or unlocking is accomplished byoperating a switch inside the door when a driver is sitting in thedriver's seat. To lock or unlock the door from outside the automobile,the driver places a key into a key hole provided in the door and turnsthe key.

Recently, systems have been used that lock or unlock the doors by remoteoperation from nearby the automobile using a remote control apparatuswhich comprises a transmitter and a receiver. The transmitter of theremote control apparatus may be provided in the grip of the ignition keyor in the key holder. The receiver is provided inside the automobile.

FIG. 11 shows a block diagram of a transmitter T and a receiver R of aremote control apparatus. The transmitter T comprises an operationcircuit 41, a decoder 42, a modulator 43, a carrier signal generator 44and a light-emitting circuit 45. The receiver R comprises alight-receiving circuit 46, an amplifier 47, a demodulator 48, a decoder49 and a code discriminating circuit 50. A door lock controller 51,connected to the code discriminating circuit 50, controls the locking orunlocking of the doors.

When a transmission switch 52, provided in the circuit 41 of thetransmitter T is depressed, an identification code (hereinafter called"ID code") stored in the transmitter T is output to the modulator 43from the decoder 42. The modulator 43 receives a carrier signal at apredetermined frequency (e.g., 38 kHz) from the carrier signal generator44. Then, the modulator 43 modulates the frequency of the ID code withthe carrier signal and outputs it as a modulation signal to thelight-emitting circuit 45. The light-emitting circuit 45 produces aninfrared signal from the modulation signal and transmits it to thereceiver R.

The light-receiving circuit 46 in the receiver R provided inside theautomobile, receives the modulated infrared-ray signal sent from thelight-emitting circuit 45 of the transmitter T, and outputs this signalto the amplifier 47. The amplifier 47 amplifies the modulated signal toa predetermined level, and outputs it to the demodulator 48. Thedemodulator 48 extracts only the ID code from the signal and demodulatesit to obtain a reception signal. This reception signal is output to thedecoder 49. The decoder 49 decodes the reception signal to a receptioncode and outputs it to the code discriminating circuit 50.

The code discriminating circuit 50 compares the reception code with adiscrimination code stored previously in the receiver R. When thereception code does not coincide with the discrimination code, the codediscriminating circuit 50 erases the reception code and stands by untilthe next reception code is input. When the reception code coincides withthe discrimination code, the code discriminating circuit 50 outputs asignal to the door lock controller 51 to unlock the doors when the doorsare locked, or another signal to lock the doors when the doors areunlocked.

Recently, Audio-Visual machines and electric home appliances can bemanipulated by a single "smart" remote controller. This "smart" or"learning" remote controller is designed to store an ID code (data)transmitted from a remote controller supplied with each machine. Thereare three ways that the learning remote controller stores the ID data ofeach machine. First, demodulation at a predetermined frequency istriggered by an operation signal from the transmitter of each machine,data compression is performed, and then the compressed data is stored ina memory area. Second, a modulation frequency is detected at thebeginning of the operation signal, all signals are demodulated at thatmodulation frequency, data compression is performed, and the compresseddata is stored in the memory area. Third, the frequency of the operationsignal sent from the transmitter is determined. If this frequency isequal to or higher than a predetermined frequency, then a modulationsystem is assumed or considered as "learned". The modulation frequencyand operation signal are demodulated and are stored in the memory areaby the learning remote controller. When the frequency of data is below aspecific frequency, it is assumed or "learned" that a baseband systemexists. The ON/OFF periods of time for each data is measured and storedin the memory by the remote controller. With regard to the transmitterof a vehicle, the ID code may easily be stored or copied by the abovemethods. This unfortunately allows people other than the owner of thevehicle to unlock the doors.

Generally, the memory area of the learning remote controller has arelatively small capacity to store compressed data. If information istransmitted that causes the capacity of the memory area to overflow, thedata cannot be stored. For the above type of learning remotecontrollers, if the signal at the beginning portion of the operationsignal has a frequency different from the modulation frequency, anysubsequent signal cannot be correctly read.

Accordingly, it is a primary objective of the present invention toprovide a remote control apparatus which prevents an identification codefrom being stored in a learning remote controller.

It is another objective of this invention to provide a remote controlapparatus which can more surely prevent an identification code frombeing stored in a learning remote controller.

DISCLOSURE OF THE INVENTION

A remote control apparatus of the present invention includes firstcarrier signal generating means for generating a first carrier signal ofa first frequency for use in the frequency modulation of anidentification code signal; transmission means for transmitting thefrequency modulated identification code signal; second carrier signalgenerating means for generating a second carrier signal of a secondfrequency different from the first frequency; and affixing means foraffixing the second carrier signal of the second frequency to thefrequency modulated identification code signal and for outputting theidentification code to the transmission means. The second carrier signalhas a length of a given time. The first carrier signal generating meansoutputs a first carrier signal of the first frequency for use in thefrequency modulation of an identification code signal. The secondcarrier signal generating means outputs a second carrier signal of thesecond frequency different from the first frequency. The affixing meansaffixes the second carrier signal to an arbitrary portion of theidentification code signal whose frequency is modulated based on thefirst carrier signal, and outputs it to the transmission means. Thefirst carrier signal including the identification code and the secondcarrier signal including no identification code exist for a given periodof time. When a smart or learning remote controller of the type whichalways performs demodulation with the first frequency tries to store theidentification code, the second carrier signal of the second frequencyis also demodulated with the first frequency and is stored after datacompression. Therefore, the second carrier signal can cause the memorycapacity of the learning remote controller to overflow. As a result, itis possible to prevent the identification code from being stolen by thelearning remote controller. When a learning remote controller of thetype which detects the modulation frequency in synchronism with the headsignal tries to store the identification code, demodulation is performedbased on either the first carrier signal of the first frequency affixedto the head or the second carrier signal of the second frequency.Accordingly, the subsequent carrier signal cannot be demodulatedcorrectly and the correct identification code cannot be detected. Thisprevents the identification code from being stolen by the learningremote controller. Further, even when a learning remote controller ofthe type which discriminates the baseband signal tries to store theidentification code, demodulation is performed after the discriminationof the baseband signal based on the signal affixed to the head as in theaforementioned case. Accordingly, the subsequent signal of a differentfrequency can cause the overflowing of the memory capacity of thelearning remote controller. This prevents the identification code frombeing stolen by the learning remote controller.

A remote control apparatus of the present invention includes firstcarrier signal generating means for generating a first carrier signal ofa first frequency for use in the frequency modulation of anidentification code signal; transmission means for transmitting thefrequency modulated identification code signal; second carrier signalgenerating means for generating a second carrier signal of a secondfrequency different from the first frequency; and affixing means foraffixing the second carrier signal to a plurality of arbitrary portionsof the frequency modulated identification code signal in such a mannerthat a total time of the second carrier signals at the plurality ofportions becomes equal to or longer than a predetermined time, andoutputting the identification code to the transmission means. Due todividing the second carrier signal whose length is equal to or longerthan a given time and affixing the divided signals to the portions ofthe frequency modulated identification code signals, a learning remotecontroller cannot extract the first carrier signal alone. Due toaffixing the second carrier signal of the second frequency whose totaltime is equal to or longer than a given time to a plurality of arbitraryportions of the frequency modulated identification code signal, thememory capacity of the learning remote controller can surely be made tooverflow. Further, since the second carrier signal is affixed to anarbitrary portion of the first carrier signal, it is difficult for thelearning remote controller to store only the identification code. As aresult, it is possible to prevent the identification code from beingstolen by the remote controller.

A remote control apparatus of this invention includes first carriersignal generating means for generating a first carrier signal of a firstfrequency for use in the frequency modulation of an identification codesignal; transmission means for transmitting the frequency modulatedidentification code signal; reception means for receiving theidentification code signal sent from the transmission means; secondcarrier signal generating means for generating a second carrier signalof a second frequency, the second frequency lying within an attenuationregion of a reception sensitivity of the reception means; and affixingmeans for affixing the second carrier signal to the frequency modulatedidentification code signal and outputting the identification code to thetransmission means. The second carrier signal has a length of a giventime. The first carrier signal generating means outputs a first carriersignal of the first frequency for use in the frequency modulation of theidentification code signal. The second carrier signal generating meansoutputs a second carrier signal at the second frequency which lieswithin the attenuation region of the reception sensitivity of thereception means. The affixing means affixes the second carrier signal toan arbitrary portion of the identification code signal whose frequencyis modulated based on the first carrier signal, and outputs it to thetransmission means. As the second carrier signal is attenuated by thereception means, only the first carrier signal including theidentification code is extracted. It is not necessary for conventionalreceivers to be modified, therefore, a significant cost-up can beprevented.

A remote control apparatus of this invention includes first carriersignal generating means for generating a first carrier signal of a firstfrequency for use in the frequency modulation of an identification codesignal; transmission means for transmitting the frequency modulatedidentification code signal; and reception means for receiving theidentification code signal sent from the transmission means; secondcarrier signal generating means for generating a second carrier signalof a second frequency lying within an attenuation region of a receptionsensitivity of the reception means; and affixing means for affixing thesecond carrier signal to a plurality of arbitrary portions of thefrequency modulated identification code signal in such a manner that atotal time of the second carrier signals at the plurality of portionsbecomes equal to or longer than a predetermined time, and outputting theidentification code to the transmission means. The second carriersignal, the second frequency of which lies within the attenuation regionof the reception sensitivity of the reception means, is divided into aplurality of signal segments. They are affixed to a plurality ofarbitrary portions of the frequency modulated identification codesignal. Therefore, the second carrier signal can make the memorycapacity of the learning remote controller surely overflow. Since thesecond carrier signal, which as a whole becomes equal to or longer thana given time, is affixed to a plurality of arbitrary portions of thefirst carrier signal, it is difficult for a learning remote controllerto store only the first carrier signal including the identificationcode. As a result, it is possible to prevent the identification codefrom being stolen by the remote controller.

In the remote control apparatus of this invention, the affixing meansaffixes the second carrier signal to a head of the frequency modulatedidentification code signal and outputs the identification code signal tothe transmission means. As the second carrier signal is affixed to thehead of the identification code signal, the setting of the time foraffixing the second carrier signal is easy. Further, by distinguishingthe first carrier signal from the second carrier signal, which has beenaffixed to the head and does not include the identification code, at thetime a transmission signal is received by the reception means, theidentification code alone can easily be extracted without correcting theextracted identification code. Furthermore, the learning remotecontroller, which synchronizes with the head signal and detects theidentification code signal based on the synchronized modulationfrequency, performs demodulation based on the second carrier signal ofthe second frequency which has come to the head. Therefore, thesubsequent carrier signal of the first frequency cannot be demodulatedaccurately. This prevents the identification code from being memorizedby the learning remote controller.

A remote control apparatus of this invention includes first carriersignal generating means for generating a first carrier signal of a firstfrequency for use in the frequency modulation of a plurality ofidentification code signals; transmission means for transmitting thefrequency modulated identification code signals; second carrier signalgenerating means for generating a second carrier signal of a secondfrequency different from the first frequency; and affixing means foraffixing the second carrier signal to each of the plurality of frequencymodulated identification code signals, and outputting the identificationcode signals to the transmission means. The first carrier signalgenerating means outputs a first carrier signal of the first frequencyfor use in the frequency modulation of a plurality of identificationcode signals. The second carrier signal generating means outputs asecond carrier signal whose frequency is different from the firstfrequency. The affixing means affixes the second carrier signal to eachof the plurality of frequency modulated identification code signals, andoutputs it to the transmission means.

When a plurality of identification code signals are to be transmitted,the second carrier signal of the second frequency is affixed to each ofthe identification code signals, thus making it difficult to extractonly the first carrier signal including the identification code. It istherefore possible to prevent the identification code from being stolenby a learning remote controller. Further, the learning remotecontroller, which synchronizes with the head signal and stores theidentification code signal based on the synchronized modulationfrequency, performs demodulation based on the carrier signal of thefirst frequency or the second frequency. Accordingly, the subsequentcarrier signal cannot be demodulated correctly and the identificationcode cannot be stored accurately.

A remote control apparatus of this invention includes first carriersignal generating means for generating a first carrier signal of a firstfrequency for use in the frequency modulation of a plurality ofidentification code signals; transmission means for transmitting thefrequency modulated identification code signals; reception means forreceiving the identification code signals sent from the transmissionmeans; second carrier signal generating means for generating a secondcarrier signal of a second frequency lying within an attenuation regionof a reception sensitivity of the reception means; and affixing meansfor affixing the second carrier signal to each of the plurality offrequency modulated identification code signals, and outputting theidentification code signals to the transmission means. The first carriersignal generating means outputs the first carrier signal of the firstfrequency for use in the frequency modulation of the plurality ofidentification code signals. The second carrier signal generating meansoutputs the second carrier signal of the second frequency which lieswithin the attenuation region of the reception sensitivity of thereception means. The affixing means affixes the second carrier signal toeach of the plurality of frequency modulated identification codesignals, and outputs it to the transmission means. As the second carriersignal is attenuated by the reception means, it is easy to distinguishthe second carrier signal from the first carrier signal including theidentification code. It is therefore easy to extract only theidentification code without correcting the extracted identificationcode.

A remote control apparatus of this invention includes first carriersignal generating means for generating a first carrier signal of a firstfrequency for use in the frequency modulation of a plurality ofidentification code signals; transmission means for transmitting thefrequency modulated identification code signals; second carrier signalgenerating means for generating a second carrier signal of a secondfrequency different from the first frequency; and affixing means foraffixing the second carrier signal to a plurality of arbitrary portionsof each frequency modulated identification code signal in such a mannerthat a total time of the second carrier signal at the plurality ofportions becomes equal to or longer than a predetermined time, andoutputting the identification code signal to the transmission means. Thefirst carrier signal generating means outputs a first carrier signal ofthe first frequency for use in the frequency modulation of the pluralityof identification code signals. The second carrier signal generatingmeans outputs a second carrier signal of the second frequency differentfrom the first frequency. The affixing means divides the second carriersignal, whose length is equal to or longer than a given time, into aplurality of signal segments, affixes these signal segments of thesecond carrier signal to arbitrary portions of each frequency modulatedidentification code signal to be output to the transmission means. Thereexists the second carrier signal which as a whole becomes a given timewith respect to the first carrier signal including the identificationcode. When the learning remote controller of the type which detects themodulation frequency in synchronism with the head signal tries to storethe identification code, therefore, the remote controller performsdemodulation based on either the first carrier signal or the secondcarrier signal. Accordingly, the subsequent carrier signal cannot bedemodulated correctly so that the learning remote controller cannotdetect the accurate identification code. When a learning remotecontroller of the type which always performs demodulation with the firstfrequency tries to store the identification code signal, the learningremote controller demodulates the second carrier signal also with thefirst frequency and attempts to store its demodulated signal after datacompression. As a result, the memory capacity of the learning remotecontroller overflows, so that the identification code can be preventedfrom being stolen.

In the remote control apparatus of this invention, the affixing meansaffixes the second carrier signal to a head of each of the plurality offrequency modulated identification code signals, and outputs theidentification codes to the transmission means.

The first carrier signal generating means outputs a first carrier signalof the first frequency for use in the frequency modulation of aplurality of identification code signals. The second carrier signalgenerating means outputs a second carrier signal of the secondfrequency. The affixing means affixes the second carrier signal to thehead of each of the plurality of frequency modulated identification codesignals and outputs it to the transmission means. When a plurality ofidentification code signals are transmitted, the second carrier signalis affixed to the head of each identification code signal. This makes itdifficult to extract only the first carrier signal including theidentification code. Further, a smart or learning remote controller,which synchronizes with the head signal and stores the identificationcode based on the modulation frequency, performs demodulation based oneither the first carrier signal or the second carrier signal. Therefore,the subsequent carrier signal cannot be demodulated accurately, and thelearning remote controller cannot store the accurate identificationcode. It is thus possible to prevent the identification code from beingstolen by the learning remote controller.

In the remote control apparatus of this invention, one of the firstcarrier signal generating means and the second carrier signal generatingmeans is means for dividing or multiplying the frequency of a signaloutput from the other one. One of the first and second carrier signalgenerating means divides or multiplies the frequency the signal from theother one. By making a simple modification to one carrier signalgenerating means, therefore, the other carrier generating means can beprovided, eliminating the need for an oscillator in each signalgenerating means. This can contribute to simplifying the remote controlapparatus and making it compact.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a transmitter and receiver of a remotecontrol apparatus according to the present invention;

FIG. 2 is a perspective view showing a key holder, an ignition key andthe receiver;

FIG. 3 is an explanatory diagram showing input and output signals of amodulator in a first embodiment of the invention;

FIG. 4 is a diagram showing the frequency-gain characteristic of afilter circuit incorporated in a demodulator;

FIG. 5 is an explanatory diagram showing input and output signals of amodulator in a second embodiment of the invention;

FIG. 6 is an explanatory diagram explaining how a learning remotecontroller stores an ID code;

FIG. 7 is an explanatory diagram explaining how a learning remotecontroller stores an ID code;

FIG. 8 is an explanatory diagram illustrating the input and outputsignals of another modulator based on the second embodiment;

FIG. 9 is an explanatory diagram illustrating the input and outputsignals of yet another modulator based on the second embodiment;

FIGS, 10A, 10B and 10C are block diagrams illustrating essentialportions of transmitters of remote controllers according tomodifications of the invention; and

FIG. 11 is a block diagram illustrating a transmitter and a receiver ofa conventional remote control apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment)

A remote control apparatus for a vehicle according to a first embodimentof the present invention will be described below with reference to FIGS.1 through 4.

As shown in FIG. 2, a transmitter T is incorporated in a key holder 1. Apush button 2 is provided on the top of the key holder 1. Provided atthe front face of the key holder 1 is a light-emitting section 3comprising an infrared signal emitting element. A receiver R is providedinside an unillustrated vehicle.

As shown in FIG. 1, the transmitter T comprises an operation circuit 11,a decoder 12, an ID code memory 13, a modulator 14, a first carriersignal generator 15, a second carrier signal generator 16, and alight-emitting circuit 17 as a transmission means. The modulator 14 andthe second carrier signal generator 16 form an affixing means.

The operation circuit 11 is provided with the push button 2. The decoder12 is connected to the operation circuit 11, which outputs a depressionor activation signal to the decoder 12 by the operation of the pushbutton 2.

The ID code memory 13 and modulator 14 are connected to the decoder 12.The ID code memory 13 is a non-volatile memory device in which apreviously set ID code S is stored. When the depression signaloriginating from the operation of the push button 2 is input to thedecoder 12, the decoder 12 reads the ID code S from the ID code memory13, and outputs it to the modulator 14 after serial-parallel conversion.

The first carrier signal generator 15, the second carrier signalgenerator 16 and the light-emitting circuit 17 are connected to themodulator 14. The first carrier signal generator 15 generates a firstcarrier signal S1 at a predetermined frequency f_(M) (38 kHz in thisembodiment) and outputs it to the modulator 14. The second carriersignal generator 16 generates a second carrier signal S2 at a frequencyf_(MA), which is the frequency of the first carrier signal S1 divided byα (divided by 4 to be 9.5 kHz in this embodiment). The generator 16 thenoutputs it to the modulator 14.

When the push button 2 is operated, the second carrier signal generator16 outputs the second carrier signal S2 to the modulator 14. The secondcarrier signal S2 is frequency-modulated and is output as a modulationsignal H2, as it is, to the light-emitting circuit 17 for a given time.Thereafter, the first carrier signal generator 15 outputs the firstcarrier signal S1 to the modulator 14. The modulator 14 modulates thefrequency of the ID code S based on this first carrier signal S1, andoutputs modulation signal H1 of the ID code S to the light-emittingcircuit 17.

The light-emitting circuit 17 is provided with the light-emittingsection 3. The light-emitting circuit 17 causes the light-emittingsection 3 to emit light based on the input of the modulation signals H1and H2 from the modulator 14. The light-emitting circuit then transmitsthe modulation signals H1 and H2 by an infrared signal.

The structure of the receiver R will now be discussed.

As shown in FIG. 1, the receiver R comprises a light-receiving circuit21, an amplifier 22, a demodulator 23, a decoder 24 and a codediscriminating circuit 25.

The light-receiving circuit 21 is provided with a light-receivingelement 26. The amplifier 22 is connected to the light-receiving circuit21. When the light-receiving element 26 receives the infrared signalsent from the light-emitting section 3 of the transmitter T, thelight-receiving circuit 21 converts the signal to an electric signal andoutputs it to the amplifier 22.

The demodulator 23 is connected to the amplifier 22. The signal receivedby the light-receiving element 26 is input to the amplifier 22. Theamplifier 22 amplifies the input signal to a level suitable for thedemodulator 23, and then outputs the amplified signal to the demodulator23.

The decoder 24 is connected to the demodulator 23. The demodulator 23incorporates a filter circuit 27. The amplified modulation signals H1and H2 are input to this filter circuit 27. The signal output from thefilter circuit 27 alone is demodulated by the demodulator 23. The filtercircuit 27 is set in such a way as to maximize the gain of the carriersignal S1 at the frequency f_(M) and to reduce the gain of the secondcarrier signal S2 at the frequency f_(MA), as shown in FIG. 4. Thesignal S2 is in this way attenuated. The frequency that falls in theattenuation region of the filter circuit 27 is selected at the time thefrequency f_(MA) of the second carrier signal S2 is set.

Therefore, the frequency f_(MA) component of the second carrier signalS2 in the modulation signal H2 is attenuated by the filter circuit 27,but is not extracted. Only the frequency f_(M) component of the firstcarrier signal S1 in the modulation signal H1 is extracted (output) fromthe filter circuit 27, and the modulation signal H1 is demodulated bythe demodulator 23. The demodulator 23 outputs the demodulated ID code Sas a reception signal to the decoder 24.

The code discriminating circuit 25 is connected to the decoder 24. Thedecoder 24 performs serial-parallel conversion on the reception signalof the ID code S output from the demodulator 23, and outputs it as areception code S4 to the code discriminating circuit 25.

An ID code memory 28 and a door lock controller 29 are connected to thecode discriminating circuit 25. A discrimination code S5 is preset inthe ID code memory 28. This discrimination code S5 matches with theaforementioned ID code S. When receiving the reception code S4, the codediscriminating circuit 25 reads the discrimination code S5 stored in theID code memory 28 and compares the reception code S4 with thediscrimination code S5. When the reception code S4 matches thediscrimination code S5, the code discriminating circuit 25 outputs adoor lock control signal S6 to the door lock controller 29 to lock orunlock the doors.

A description will now be given of the action of the remote controlapparatus.

A driver approaches an automobile and pushes the push bottom 2 of thekey holder 1 to unlock the doors. The operation circuit 11 of thetransmitter T, incorporated in the key holder 1, outputs a depressionsignal to the decoder 12 based on the operation of the push button 2.Then, the second carrier signal generator 16 outputs the second carriersignal S2 at the frequency f_(MA) to the modulator 14 for a preset time.The modulator 14 modulates the frequency of the second carrier signal S2directly and outputs it to the light-emitting circuit 17.

The decoder 12 reads the ID code S stored in the ID code memory 13 inresponse to the depression signal. The decoder 12 performsserial-parallel conversion on the read ID code S, and outputs it to thedecoder 12 after the second carrier signal S2 has stopped being outputto the modulator 14. The first carrier signal generator 15 outputs thefirst carrier signal S1 at the frequency f_(M) to the modulator 14either at the same time the ID code S is output to the modulator 14 fromthe decoder 12 or after the second carrier signal S2 has stopped beingoutput to the modulator 14.

When receiving the ID code S and first carrier signal S1, the modulator14 modulates the frequency of the ID code S based on this first carriersignal S1 and outputs it as the modulation signal H1 to thelight-emitting circuit 17. The light-emitting circuit 17 causes thelight-emitting section 3 to emit light based on the input modulationsignals H1 and H2 and sends it as an infrared ray to the receiver R.

The light-receiving circuit 21 of the receiver R receives the infraredsignal, sent from the transmitter T, at the light-receiving element 26.The light-receiving circuit 21 converts the infrared signal to anelectric signal, and outputs the modulation signals H1 and H2 to theamplifier 22. The amplifier 22 amplifies the modulation signals H1 andH2 to a level necessary for input to the demodulator 23. These amplifiedsignals are then output to the demodulator 23. The frequency f_(MA)component of the second carrier signal S2 in the modulation signal H1and H2 is attenuated by the filter circuit 27 of the demodulator 23 sothat only the frequency f_(M) component of the first carrier signal S1is extracted. The demodulator 23 demodulates the modulation signal H1,extracted by the filter circuit 27, and outputs it to the decoder 24.The decoder 24 performs serial-parallel conversion on the demodulatedsignal to produce the input ID code S, and then outputs it as thereception code S4 to the code discriminating circuit 25.

The code discriminating circuit 25 compares the input reception code S4with the discrimination code S5 stored in the ID code memory 28. At thistime, the reception code S4 coincides with the discrimination code S5.As a result, the code discriminating circuit 25 outputs the door lockcontrol signal S6 to the door lock controller 29. In response to thedoor lock control signal S6, the door lock controller 29 locks orunlocks the doors.

The remote control apparatus of this embodiment affixes, the secondcarrier signal S2 set at the frequency f_(MA) to the beginning of IDcode S. The frequency f_(MA) of the second carrier signal S2 isdifferent from the frequency f_(M) of the first carrier signal S1. Theremote control apparatus then transmits ID code S from the transmitterT.

At the time the "smart" remote controller, of the type which performsdemodulation at a predetermined frequency, begins to store the ID codeS, demodulation and data compression are performed based on thefrequency f_(M) of the first carrier signal S1. If the second carriersignal S2 is, at the same time, demodulated at frequency f_(M) and ifdata compression is performed, an excessively large area will berequired. As a result, the memory capacity of the learning remotecontroller overflows.

When the learning remote controller, of the type which detects themodulation frequency at the beginning of the operation signal, begins tostore the ID code, demodulation is performed based on the frequencyf_(MA) of the second carrier signal S2 affixed to the beginning of theoperation signal. This makes it impossible to accurately read the IDcode S modulated by the frequency f_(M) of the first carrier signal S1.

Accordingly, it is possible to prevent the ID code S from being storedin any of the above two learning remote controllers.

A brief description will be given of how the memory capacity of thelearning remote controller overflows if the frequencies of themodulation signals H1 and H2 sent from the transmitter T differ fromeach other.

Referring to FIG. 6, a "smart" remote controller (not shown) is set to alearning mode, and the transmitter T is directed to the learning remotecontroller. When the push button 2 of the transmitter is operated, theID code S is modulated based on the frequency of the first carriersignal S1 at 38 kHz and then transmitted to the "smart" remotecontroller. The remote controller determines the frequency with whichthe ID code S has been modulated. Upon determining that the frequency is38 kHz, the learning remote controller measures the time period duringwhich the modulation signal H1 is at a H level (high potential) or at aL level (low potential), based on a reference pulse T0.

In this case, the individual periods of time of the modulation signal H1are illustrated as 5T0, 2T0, 2T0, 3T0, 2T0, 3T0, 1T0, 1T0 and 2T0. Theremote controller stores these periods of time in memory. Thereafter,when the remote controller is operated it transmits the modulationsignal H1 corresponding to these time periods.

As shown in FIG. 7, when the ID code S is transmitted based on thecarrier signal of 15 kHz or lower, the remote controller measures theON/OFF duration of the light-emitting section 3. As shown in FIG. 7, theperiods of time are t10, t11, t12, t13, t14, t15, t16 and t17. Theremote controller then stores these times t10 to t17 in memory. Uponfurther operation, the remote controller controls the ON/OFF operationof its light-emitting section 3 based on the times t10 to t17 andtransmits the ID code S.

When the second carrier signal S2 of 9.5 kHz is affixed at the beginningof the ID code S, the controller initiates a mode of operation tomeasure the time during which the light-emitting section 3 is on or off.After this time, when the modulation signal H1 is transmitted, theON/OFF times for each cycle of the modulation signal H1 consequentlymeasured. When the frequency of the first carrier signal S1 is high, thenumber of ON/OFF times which have to be stored increases. Because thememory area of the controller cannot store all the ON/OFF times of themodulation signal H1, memory overflow occurs. The result is that ID codeS is prevented from being stored in the learning remote controller.

Since the frequency f_(MA) of the second carrier signal S2 is 1/α thefrequency f_(M) of the first carrier signal S1, signal S2 can begenerated by a simple circuit. In addition, the frequency f_(MA) is setto comply with the frequency gain characteristics of the filter circuit27. Consequently, only the reception signal modulated with the firstcarrier signal S1 can be extracted from the modulation signals H1 and H2without having to modify the receiver R.

(Second Embodiment)

A second embodiment of the present invention will now be described.Since the structure of the transmitter T and receiver R are the same asthose of the first embodiment, reference will be made to FIG. 1, withoutredescribing their structure.

When the operation circuit 11 outputs the depression or activationsignal to the decoder 12 in response to the operation of the push button2, the decoder 12 reads the ID code S from the ID code memory 13,performs serial-parallel conversion on the ID code S three timesfollowing a predetermined time t1, and outputs it to the modulator 14,as shown in FIG. 5. Individual data segments of the ID code S arepreviously determined as time intervals t2 to t6. Period of time t7 is atime interval from when the output of the first ID code S to themodulator 14 is completed to when the output of the second ID code Sbegins, while period of time t8 is a time interval from when the outputof the second ID code S is completed to when the output of the third IDcode S begins. The time periods t7 and t8 are also determinedpreviously. In this embodiment, time period t7 is set equal to timeperiod t8.

When the predetermined time t1 passes after depression signal is outputfrom the operation circuit 11 to the decoder 12, the second carriersignal generator 16 outputs the second carrier signal S2 at thefrequency f_(MA) (9.5 kHZ in this embodiment), which is 1/α thefrequency f_(M) of the modulator 14 for a given time (several tens ofmilliseconds in this embodiment).

During the time period t7 from when the first ID code S is output to themodulator 14 from the decoder 12 to when the output of the second IDcode S to the modulator 14, the second carrier signal generator 16outputs the second carrier signal S2 at the frequency f_(MA) to themodulator 14 for a given time. Likewise, during the time period t8, thesecond carrier signal generator 16 outputs the second carrier signal S2at the frequency f_(MA) to the modulator 14.

During the time t2-t6 when the decoder 12 outputs each of the first tothird ID codes S, the first carrier signal generator 15 outputs thefirst carrier signal S1 to the modulator 14. While the output of thefirst carrier signal S1 to the modulator 14 can be slightly longer thanthe period t2-t6 during the output of a single ID code S, the period ofcarrier signal S1 is set not to overlap that of the second carriersignal S2.

Therefore, the frequency of the second carrier signal S2 is modulateddirectly by the modulator 14 into the modulation signal H2, which isoutput to the light-emitting circuit 17. The frequency of each ID code Sis modulated, based on the first carrier signal S1, into the modulationsignal H1, which is output to the light-emitting circuit 17. Thelight-emitting circuit 17 causes the light-emitting section 3 to emitlight based on the modulation signals H1 and H2 input from the modulator14, and transmits the modulation signals H1 and H2 on an infrared signalto the receiver R.

Thus, in response to the operation of the push button 2, the secondcarrier signal S2 at the frequency f_(MA) is affixed to the beginning ofeach ID code S. The frequency f_(MA) of the second carrier signal S2 is1/α (1/4 in this embodiment) of the frequency f_(M) of the first carriersignal S1 and is lower than that of the first carrier signal S1. Theaffixed signal is transmitted to the receiver R from the transmitter T.

When the light-receiving element 26 in the circuit 21 receives theinfrared modulation signals H1 and H2 from the light-emitting section 3,the light-receiving circuit 21 converts the modulation signals H1 and H2to electric signals and outputs them to the amplifier 22. The amplifier22 amplifies the electric modulation signals H1 and H2 to a levelsuitable for the demodulation of the demodulator 23, and outputs them tothe demodulator 23.

Of the amplified modulation signals H1 and H2, the modulation signal H2which becomes the second carrier signal S2 is attenuated by the filtercircuit 27, and only the modulation signal H1 which becomes the firstcarrier signal S1 is extracted. The demodulator 23 demodulates thismodulation signal H1. The demodulator 23 outputs the demodulated ID codeS as a reception signal to the decoder 24. The decoder 24 performsserial-parallel conversion on the reception signal and outputs it as thereception code S4 to the code discriminating circuit 25.

When receiving the reception code S4 from the decoder 24, the codediscriminating circuit 25 reads the discrimination code S5 from the IDcode memory 28 and determines whether or not the reception code S4coincides with the discrimination code S5. When the reception code S4does not match with the discrimination code S5, the code discriminatingcircuit 25 determines that the ID code S is different, clears thereception code S4 output from the decoder 24, and waits for a newreception code S4 output from the decoder 24.

When the reception code S4 matches with the discrimination code S5, thecode discriminating circuit 25 determines that the correct ID code S hasbeen transmitted, and outputs the door lock control signal S6 to thedoor lock controller 29 to lock or unlock the doors.

A description will now be given of the action of the thus constitutedremote control apparatus.

A driver approaches an automobile and pushes the push button 2 of thekey holder 1 to unlock the doors. The operation circuit 11 of thetransmitter T, incorporated in the key holder 1, outputs a depression oractivation signal to the decoder 12 in response to the operation of thepush button 2. Then, the decoder 12 reads the ID code S stored in the IDcode memory 13. Meanwhile, the second carrier signal generator 16outputs the second carrier signal S2 at the frequency f_(MA) to themodulator 14 for a given time, during the time from when the output ofthe depression signal begins to when a predetermined time t1 haselapsed. The frequency of the second carrier signal S2 is modulated bythe modulator 14 into the modulation signal H2, which is output to thelight-emitting circuit 17. The light-emitting circuit 17 causes thelight-emitting section 3 to emit light in response to the modulationsignal H2, and sends the modulation signal H2 on an infrared ray to thereceiver R.

When the predetermined time t1 elapses after the input of the depressionsignal to the decoder 12, the decoder 12 outputs the first ID code S tothe modulator 14. While the decoder 12 is outputting the ID code S tothe modulator 14, i.e., during times t2-t6, the first carrier signalgenerator 15 outputs the first carrier signal S1 to the modulator 14.The modulator 14 modulates the frequency of the ID code signal S inaccordance with the first carrier signal S1, and outputs it as themodulation signal H1 to the light-emitting circuit 17. Thelight-emitting circuit 17 causes the light-emitting section 3 to emitlight in accordance with the modulation signal H1, and sends themodulation signal H1 on an infrared ray to the receiver R.

During the time from the transmission of the first ID code S as themodulation signal H1 to when the time t7 elapses, the second carriersignal generator 16 outputs the second carrier signal S2 to themodulator 14. This second carrier signal S2 becomes the modulationsignal H2 to be transmitted to the receiver R, in the same manner asdescribed above. When the time t7 elapses and at the same time orslightly before the second ID code S is output to the modulator 14, thefirst carrier signal generator 15 outputs the first carrier signal S1 tothe modulator 14. While the ID code signal S is being output to themodulator 14, this first carrier signal S1 is also output to themodulator 14. The modulator 14 modulates the frequency of the ID codesignal S into the modulation signal H1 based on the first carrier signalS1, and outputs the modulation signal H1 to the light-emitting circuit17. The light-emitting circuit 17 causes the light-emitting section 3 toemit light based on the modulation signal H1, and sends the modulationsignal H1 on an infrared ray to the receiver R.

During the time from the transmission of the second ID code signal asthe modulation signal H1 to when the time t8 passes, the second carriersignal S2 is output to the modulator 14. This second carrier signal S2becomes the modulation signal H2 to be transmitted to the receiver R inthe same manner as described above. When the time t8 passes, the decoder12 and the first carrier signal generator 15 respectively output thethird ID code S and the first carrier signal S1 to the modulator 14, inthe same manner as described above. The modulator 14 modulates thefrequency of the ID code signal S based on the first carrier signal S1.

Thus, the light-emitting circuit 17 transmits the infrared modulationsignals H1 and H2, sequentially output from the modulator 14, to thereceiver R from the light-emitting section 3.

The modulation signals H1 and H2, sequentially sent from the transmitterT to the light-receiving element 26, are converted to electric signalsby the light-receiving circuit 21 and are amplified by the amplifier 22.The amplified modulation signals H1 and H2 are output to the filtercircuit 27 of the demodulator 23. The modulation signal H2 of thefrequency f_(MA) is attenuated by the filter circuit 27, and only themodulation signal H1 of the frequency f_(M) is extracted. Thedemodulator 23 demodulates the extracted modulation signal H1. Thedemodulator 23 outputs the demodulated ID code signal S as the receptionsignal to the decoder 24. The decoder 24 performs serial-parallelconversion on the reception signal, and outputs it as the reception codeS4 to the code discriminating circuit 25.

When receiving the reception code S4 from the decoder 24, the codediscriminating circuit 25 reads the discrimination code S5 from the IDcode memory 28 and determines whether or not the reception code S4matches with the discrimination code S5. When the reception code S4 doesnot coincide with the discrimination code S5, the code discriminatingcircuit 25 determines that the codes are different from each other,clears the reception code S4 output from the decoder 24, and waits for anew reception code S4 output from the decoder 24.

When the reception code S4 matches with the discrimination code S5, thecode discriminating circuit 25 determines that the correct ID code S hasbeen transmitted, and outputs the door lock control signal S6 to thedoor lock controller 29 to lock or unlock the doors.

According to the second embodiment, in the case where a plurality of IDcodes S are transmitted to the receiver R from the transmitter T, thesecond carrier signals S2 each having a different frequency are affixedto the beginnings of the individual ID codes S for a given time.

In a transmitter T by which a second carrier signal S2 is affixed onlyto the beginning of the first ID code S, it is possible that the secondor third ID code S from the transmitter T is timely stored or stolen bya smart or learning remote controller after the transmission of thesecond carrier signal S2. If the second carrier signal S2 is affixed tothe beginning of each ID code signal S, therefore, it will be difficultthat the learning remote controller receives only the ID code Sexcluding the second carrier signal S2. This surely prevents the ID codeS from being stored in the remote controller.

In order to make the memory capacity of the learning remote controllerto overflow and to prevent the ID code S from being stolen, it isdesirable that the frequency of the second carrier signal S2 be equal toor lower than 15 kHz. When the second carrier signal S2 has a frequencyof 9.5 kHz, 128 or more pulse signals should be read into the learningremote controller to cause the overflow of the memory capacity. Thelower the frequency becomes, the longer the time for outputting 128 ormore pulses becomes.

According to the second embodiment, however, since the time intervalssuch as t1, t7 and t8 between ID codes transmission periods can beeasily changed as desired, 128 or more pulse signals can surely beaffixed to the beginning of each ID code signal S. This causes theoverflow of the memory capacity of the learning remote controller, thuspreventing the ID code S from being stolen.

In the second embodiment, if a learning remote controller first detectsa middle portion of the first or second modulation signal H1,originating from the first carrier signal S1, it enters the mode formeasuring the H-level and L-level durations of the modulation signal H1as shown in FIG. 6. However, the ID code signal S based on themodulation signal H1 cannot be stored correctly. In this case, thelearning remote controller attempts to store the modulation signal H1 tobe transmitted next. Before the remote controller receives the nextmodulation signal H1 as the next ID code signal S, however, themodulation signal H2 of the second carrier signal S2 is input to theremote controller. This carrier signal S2 has 128 or more pulse signals.Therefore, if the learning remote controller measures the L-level andH-level durations of the second carrier signal S2, its memory capacitywill overflow so that the transmitted ID code S cannot be storedaccurately. It is thus possible to surely prevent the ID code S frombeing stolen by the learning remote controller.

Although the second carrier signal S2 is affixed to the beginning orhead portion of each ID code S for a given time in the secondembodiment, the following modifications are possible.

As shown in FIG. 8, the period of time t1 is a time from when the pushbutton 2 is manipulated to when the first ID code S is output to themodulator 14 from the decoder 12, and the periods of time t7 and t8 aretime intervals from the transmission of each ID code S to thetransmission of the next ID code S. The time periods t1, t7 and t8 andthe time intervals t2-t6 of individual data of the ID code S arepredetermined. The second carrier signal generator 16 is set to send anoutput to the modulator 14 even during the time where the data of one IDcode S becomes an L level (time t3, t5 in this case). Then, themodulation signal H2 is output even when the modulation signal H1becomes an L level.

As the L-level duration of each ID code S is short, it is difficult toaffix the second carrier signal S2 every such L-level duration for asufficient time to cause the overflow of the memory capacity of thelearning remote controller. Accordingly, the second carrier signal S2which has a length of a given time is multi-segmented. The division isperformed in such a way that the segmented second carrier signal S2 doesnot overlap the H level of data in the ID code S. When the first ID codeS is output to the modulator 14, the second carrier signal generator 16outputs the second carrier signal S2, divided at the predetermined timet1, to the modulator 14. Then, the second carrier signal S2 divided atthe time t3 is output to the modulator 14. Further, the second carriersignal S2 divided at the time t5 is output to the modulator 14.

The total time of the second carrier signals S2 divided at the times t1,t3 and t5 is set equal to the set time in the second embodiment, duringwhich 128 or more pulses are generated.

When the second ID code signal S is output to the modulator 14, thesecond carrier signal generator 16 outputs the second carrier signal S,divided at the time t7, to the modulator 14, and thereafter outputs thesecond carrier signals S2 divided at the times t3 and t5 of the ID codeS, to the modulator 14. Likewise, when the third ID code S is output tothe modulator 14, the second carrier signal generator 16 outputs thesecond carrier signal S2, divided at the time t8, to the modulator 14,and thereafter outputs the second carrier signals S2 divided at thetimes t3 and t5 of the ID code S, to the modulator 14.

Therefore, the modulator 14 directly modulates the frequencies of thesequentially input second carrier signals S2. The modulated signals aretransmitted as the modulation signals H2 to the receiver R from thelight-emitting section 3 of the light-emitting circuit 17. The frequencyof the ID code signal S is modulated based on the first carrier signalS1, and the modulated ID code signal S is transmitted as the modulationsignal H1 to the receiver R from the light-emitting section 3 of thelight-emitting circuit 17. The receiver R receives the modulationsignals H1 and H2 sequentially transmitted over infrared rays, and thedoors are locked or unlocked in the same manner as done in theabove-described second embodiment.

In this modification, the second carrier signals S2, each of which has alength of a given time, are affixed to arbitrary portions of the ID codesignal S. It is therefore difficult for a smart or learning remotecontroller to read only the modulation signal H1 cocorresponding to theID code S. It is thus possible to more surely prevent the ID code S frombeing stolen by learning remote controllers.

When a learning remote controller detects the modulation signal H2 basedon the second carrier signal S2 first, it measures the ON/OFF times ofthe light-emitting section 3 in the light-emitting circuit 17. Further,the remote controller detects and memorize the ON/OFF switching times ofthe light-emitting section 3 based on the first carrier signal S1. Thiscauses the overflow of the memory capacity of the learning remotecontroller as per the second embodiment. Consequently, the ID code S canbe prevented from being stolen by the learning remote controller.

When the learning remote controller detects the modulation signal H1based on the first carrier signal S1 first, it measures the H-level andL-level durations of the modulation signal H1 sent from thelight-emitting section 3 referring to the reference pulse T0.Accordingly, it also measures the H-level and L-level durations of themodulation signal H2 based on the second carrier signal S2, referring tothe reference pulse T0. However, the total number of pulse signals ofthe divided second carrier signals. S2 before a next ID code signal S istransmitted becomes equal to or greater than 128. Thus, the dividedsecond carrier signals S2 can surely cause the overflow of the memorycapacity of the learning remote controller. It is therefore possible tosurely prevent the ID code S from being stolen by learning remotecontrollers.

In this modification, the second carrier signal S2 is divided to aplurality of portions, which are output at the times t3 and t5 of the IDcode S. This can shorten the intervals of the elapsing time t1 and thetimes t7 and t8, or shorten the time interval for transmitting aplurality of ID code signals S.

Although the divided carrier signals S2 are output in a well-regulatedmanner at the times t3 and t5 of the ID code S in this modification, itis not limited to this case and the divided carrier signals S2 may beoutput at arbitrary points as needed. In this case, the total time ofthe divided second carrier signals S2 should become a preset period oftime for the output of one ID code signal S.

Although three ID code signals are transmitted in response to adepression or activation signal in this modification, the structure ofthe transmitter T may be modified so that the second carrier signal S2having a length of a given time is multi-segmented and themulti-segmented signals are affixed to several portions of a single IDcode signal S, wherein the single ID signal S is transmitted in responseto one depression signal.

Alternatively, the present invention may be modified as shown in FIG. 9.The times t1, t7 and t8, during which the individual ID codes S are nottransmitted, are previously determined and the time intervals t2-t6 ofthe individual data of the ID code signal S are also determinedpreviously. Therefore, the second carrier signal generator 16 dividesthe second carrier signal S2 having a length of a given time intomultiple segments. Each of the divided second carrier signal segment maybe put adjacent to the rising edge and falling edge on both sides of theH level of each data in one ID code S, so that the ID data signals andthe second carrier signal segments are continuously output. In themodification shown in FIG. 9, similar advantage and effect to those ofthe modification of the second embodiment can be obtained.

Even if the ID data signals and the second carrier signal segments arecontinuously output, the modulation signal H2 corresponding to thesecond carrier signal S2 is normally attenuated by the filter circuit 27in the demodulator 23 in the receiver R and only the modulation signalH1 corresponding to the first carrier signal S1 is extracted to bedemodulated. As shown in (A) in FIG. 9, normally, the modulation signalH1 is demodulated and only the signal equivalent to the ID code S isoutput to the decoder 24.

If the performance of the filter circuit 27 deteriorates so that themodulation signal H2 corresponding to the second carrier signal S2 isalso extracted and demodulated, the signals equivalent to the extractedsecond carrier signal segments are affixed to both sides of the signalequivalent to each ID data, as indicated in (B) in FIG. 9.

Based on the time interval tA from the rising edge of each data in theID code S to the next rising edge, the code discriminating circuit 24 ofthe receiver R determines whether that data is "0" or "1". When thesignals equivalent to the second carrier signal segments are affixed toboth sides of the signal equivalent to the ID code data, it isdetermined whether that data is "0" or "1" based on the time interval tBfrom the rising edge of the signal equivalent to a second carrier signalsegment to the rising edge of the signal equivalent to the next secondcarrier signal segment. Even in this case, time tA is equal to time tB.As a result, even if the performance of the filter circuit 27deteriorates, the transmitted ID code S can substantially be preventedfrom changing so that the lock and unlock operations of doors can beaccurately performed.

In this modification, the second carrier signal S2 which has a length ofa given time is multi-segmented, each segmented second carrier signal isput adjacent to the rising and falling edges of one ID data of each IDcode signal S. Although three of such ID code signals are sequentiallytransmitted, it may be designed such that only one ID code signal S istransmitted as needed.

Although the second carrier signal S2 which has a length of a given timeis multi-segmented and each segmented second carrier signal S2 is putadjacent to the rising and falling edges of one ID data signal, it maybe designed in such a way that each segmented second carrier signal S2is affixed to only one of the rising and falling edges of one ID datasignal.

The present invention is not limited to the above embodiments andmodifications, but may be modified as follows without departing from thespirit or scope of the invention.

(1) Although an infrared signal is used for transmission and receptionin the above embodiments, a signal with another wavelength, such as ashorter wavelength than that of infrared ray, may be used.

(2) Although the transmitter T is installed in the key holder 1 in theabove embodiments, the transmitter T may be installed in an ignition key4 as shown in FIG. 2.

(3) Although 1/α of the frequency f_(M) of the first carrier signal S1is used as the frequency f_(MA) of the second carrier signal S2 in theabove embodiments, the frequency f_(MA) may be any frequency within therange included in the attenuation region of the gain-frequencycharacteristic of the filter circuit 27 of the receiver R. If afrequency is selected as the frequency f_(MA) of the second carriersignal S2, then the filter circuit 27 should be designed to have thegain-frequency characteristic in which the attenuation region includesthat selected frequency.

(4) Although the first carrier signal generator 15 and the secondcarrier signal generator 16 are separated from each other in the aboveembodiments, the following modifications are possible.

As shown in FIG. 10A, a carrier signal generator 31 for generating thefirst carrier signal S1 and a frequency-divider 32 may be connected tothe modulator 14. The frequency-divider 32 is connected to the carriersignal generator 31. The frequency-divider 32 receives the first carriersignal S1 from the carrier signal generator 31 and generates the secondcarrier signal S2 to be output to the modulator 14.

As shown in FIG. 10B, a carrier signal generator 33 for generating thesecond carrier signal S2 and a multiplier 34 may be connected to themodulator 14. The multiplier 34 is connected to the carrier signalgenerator 33. The multiplier 34 receives the second carrier signal S2from the carrier signal generator 33 and generates the first carriersignal S1 to be output to the modulator 14.

Those circuit structures are effective when 1/α of the frequency f_(M)of the first carrier signal S1 is used as the frequency f_(MA) of thesecond carrier signal S2.

As shown in FIG. 10C, a variable carrier signal generator 35 isconnected to the modulator 14. The decoder 12 is connected to thevariable carrier signal generator 35. The variable carrier signalgenerator 35 switches its output between the first carrier signal S1 andthe second carrier signal S2 in accordance with a control signal fromthe decoder 12, and outputs one of their signals to the modulator 14.

This circuit structure is effective when an arbitrary frequency lying inthe attenuation region of the gain-frequency characteristic of thefilter circuit 27 is set as the frequency f_(MA) of the second carriersignal S2.

(5) Although the above embodiments have been described as adapted for avehicular remote control apparatus, the present invention may be adaptedfor an apparatus of opening and closing an automatic shutter provided ata garage. In this case too, there is no possibility that data is stolenby a learning remote controller and the shutter will not be illegallyopen. This improves the safety of the remote control system of theshutter.

(6) The ON time period of the divided frequency f_(MA) may be setshorter than its OFF time period. The shortened ON time can result inlower power consumption and elongate the life of the battery.

The technical concept other than that described in the appended claimsthat can be understood from the above embodiments will be given belowtogether with their advantages.

(1) A remote control apparatus including:

first carrier signal generating means for generating a carrier signal ofa first frequency used to modulate the frequency of a presetidentification code signal;

transmission means for transmitting the identification code signal whosefrequency is modulated; and

reception means for receiving the identification code signal sent fromthe transmission means, characterized in that said remote controlapparatus further includes:

second carrier signal generating means for generating a carrier signalof a second frequency, the second frequency lying in an attenuationregion of a reception sensitivity of the reception means; and

affixing means for dividing the carrier signal of the second frequencywhich has a length of a given time, into multiple signal segments,continuously affixing the divided signal segments to at least one of arising edge and a falling edge of the frequency modulated identificationcode signal, and outputting the segment affixed identification codesignal to the transmission means.

With this structure, even if the attenuation factor of the receptionmeans falls and the carrier signal of the second frequency is outputtogether with the identification code signal, it is possible toaccurately determine whether the identification code is correct or not.This is because the output cycle or period of the identification code isconstant.

We claim:
 1. A remote control system comprising:means for producing anidentification code signal, first carrier signal generating means forgenerating a first carrier signal of a first frequency, means forproducing a modulated carrier signal by modulating said first carriersignal with said identification code signal, second carrier signalgenerating means for generating a second carrier signal of a secondfrequency different from said first frequency, means for adding at leasta predetermined duration of said second carrier signal to at least aportion of said modulated carrier signal sufficient to inhibitunauthorized detection of said code signal thereby producing atransmission signal, and transmission means for transmitting saidtransmission signal.
 2. A remote control system according to claim 1,further comprising reception means for receiving said transmissionsignal and detecting said identification code signal by filtering outsaid second carrier signal and demodulating said modulated carriersignal.
 3. A remote control system according to claim 2, wherein thetotal duration of said second carrier signal is sufficient to inhibitinterception of said code signal by a learning remote controller.
 4. Aremote control system according to claim 1, wherein the total durationof said second carrier signal is sufficient to inhibit interception ofsaid code signal by a learning remote controller.
 5. A remote controlsystem according to claim 1, wherein said second carrier signal is addedto a plurality of portions of said modulated carrier signal with a totalduration sufficient to inhibit said unauthorized detection of said codesignal.
 6. A remote control system according to claim 5, furthercomprising reception means for receiving said transmission signal anddetecting said identification code signal by filtering out said secondcarrier signal and demodulating said modulated carrier signal.
 7. Aremote control system according to claim 1 or 2, wherein saidpredetermined duration of said second carrier signal is added to saidmodulated carrier signal at the beginning of said identification codesignal.
 8. A remote control system according to claim 1 or 2, whereinsaid first carrier signal is modulated repeatedly with saididentification code signal to produce a plurality of modulated codesignals on said modulated carrier signal.
 9. A remote control systemaccording to claim 8, wherein said second carrier signal is added to aplurality of portions of said modulated carrier signal with a totalduration sufficient to inhibit said unauthorized detection of said codesignal.
 10. A remote control system according to claim 8, wherein saidsecond carrier signal is added to said modulated carrier signal at thebeginning of each of said identification code signals.
 11. A remotecontrol system according to claim 1 or 2, wherein one of said carriersignal generating means comprises means for dividing or multiplying thefrequency of the signal produced by the other of said carrier signalgenerating means.
 12. A method for remote control comprising incombination the steps of:generating a first carrier signal at a firstfrequency; generating a second carrier signal at a second frequency;modulating said first carrier signal using an identification code signalto produce a modulated signal; generating and transmitting atransmission signal comprising a predetermined duration of said secondcarrier signal added to at least a portion of said modulated signalwhere said duration is chosen sufficient to inhibit unauthorizeddetection of said identification code signal; and receiving anddemodulating said transmission signal using said first carrier signal tothe exclusion of said second carrier signal for extracting saididentification code signal from said transmission signal.
 13. A methodfor remote control according to claim 12, wherein said demodulating stepfurther comprises the step of filtering out said second carrier signalfrom said transmission signal.